Conventionally, an electronic control unit (abbreviated to hereinafter as an ECU) for an airbag is received in an aluminum die casting housing with a box shape. An ECU housing 1 according to a related art will be illustrated with reference to FIGS. 1A to 1D. The ECU housing 1 includes an aluminum die casting case 2 illustrated in FIG. 1B, a control circuit board 3 (also called “a board” for simplicity) illustrated in FIG. 1C, and an iron sheet cover 4 illustrated in FIG. 1D. The aluminum die casting case 2 has an opening at a bottom thereof. The control circuit board 3 is inserted into an inside of the aluminum die casting case 2 from the opening of the aluminum die casting case 2 and fixed. The iron sheet cover 4 is made of iron, and is fixed at the opening of the aluminum die casting case 2 to cover the opening. In the ECU housing 1, when a vehicle collision is detected with an acceleration sensor (not shown) mounted to the control circuit board 3, a control operation for inflating an airbag (not shown) etc. is performed. JP 2008-41718A1 corresponding to EP 1887842A1 describes this kind of housing for an electronic control unit.
In the above-described ECU housing 1, the aluminum die casting case 2 is heavy in weight and high in manufacturing cost. In view of this, the inventor of the present application conducted a study to make a case 2 of resin. The inventor's findings will be given below. If the case 2 is simply made of resin, an impact at a time of a vehicle collision is absorbed by an elastic property of the resin of the case 2. This deteriorates a transmission of the impact to the acceleration sensor for detecting the impact. In addition, it becomes impossible to connect to ground because the resin case is electrically-nonconductive, while it is possible to connect to ground via the aluminum die casting case 2 in the above related art shown in FIGS. 1A to 1D. Problems of the transmission of the impact and the connection to ground may be solved if the iron sheet cover 4 is provided with multiple stays made of the same iron sheet, and the stays are fixed to the vehicle. In this case, however, since the iron sheet cover 4 is fixed to the vehicle by the multiple stays, there is a concern that the iron sheet cover 4 is deformed due to the impact at a time of vehicle collision and the board 3 is accordingly damaged.
An event data recorder (abbreviated to as “EDR”), which is a recorder for recording a data of speed, acceleration or the like before and after the collision, is mounted to the board 3. The board 3 stores the important data for investigation of a cause of the accident after the collision. In recent years, importance of this kind of accident data is increasing. If the board 3 is damaged at a time of a vehicle collision, there arises a problem that an electronic part on the board 3 is damaged, and it becomes impossible to read out a data from the EDR.